Drawn polyethylene filament tensile member

ABSTRACT

An optical fiber cord or cable comprising at least one optical fiber and at least one tensile member for reinforcing said optical fiber, said tensile member comprising at least one polyethylene filament having a viscosity average molecular weight of not less than 200,000, a tenacity of not less than 20 g/d and a tensile modulus of not less than 600 g/d.

This application is a divisional application of presently pendingapplication Ser. No. 885,817, filed July 21, 1986, which in turn is acontinuation application of application, Ser. No. 686,958, filed Dec.27, 1984, now abandoned.

The present invention is a tensile (or tension) member of polyethylene.More particularly, it relates to a tensile member comprising a filamentof ultra high molecular weight polyethylene having high tenacity andhigh tensile modulus and being useful as a reinforcing material foroptical fiber cords or cables.

An optical fiber cord or cable comprises an optical fiber as theessential part and a tensile member as the reinforcing material. Namely,a tensile member is used for preventing an optical fiber from itsbreakage which will be caused by application of excessive tensionthereto. Such tensile member is usually made of a material which isexcellent in tensile modulus and bending rigidity.

As the tensile member for optical fiber cords or cables, there haveheretofore been used metallic materials (e.g. steel wire) and also triedwere plastic materials (e.g. polyethylene fiber, polypropylene fiber,polyamide fiber, polyester fiber). In general, metallic materials havesufficiently high tenacity and high tensile modulus suitable for suchuse. However, they have a high density, and therefore the resultingtensile member is very heavy in weight. Further, they have a problem ofelectromagnetic interference due to lightning strikes. Plastic materialsdo not have drawbacks as recognized in metallic materials; i.e. they areof light weight and do not have such problem as electromagneticinterference due to lightning strikes. However, their tenacity andtensile modulus are usually lower than those of metallic materials.

Recently, there has been provided an aromatic polyamide fiber of hightensile modulus ("Kevlar" manufactured by Du Pont). In comparison withsteel wire, it is of light weight. As shown in Table 1, for instance,the weight of the aromatic polyamide fiber showing a nearly equaltenacity to that of steel wire is from 0.28 to 0.6 when the weight ofsteel wire is taken as 1 (this being referred to as "weight ratio").Thus, the aromatic polyamide fiber can provide a tensile member of hightensile modulus and light weight. In order to attain a nearly equaltenacity, however, the aromatic polyamide fiber is required to havelarger denier or diameter than steel wire. For instance, the diameterratio of the aromatic polyamide fiber to steel wire is 1.24-1.8:1.Nevertheless, the aromatic polyamide fiber having large denier ordiameter is hardly obtainable under the present technique, and in fact,the filament of the aromatic polyamide fiber now available on the marketis less than 2 denier or less than 0.014 mm in diameter. Therefore, itis practically essential for achievement of the same level of tenacitywith the aromatic polyamide fiber as steel wire to use a multiple numberof filaments, i.e. a bundle of filaments.

Unfortunately, however, the tensile member using a bundle of filamentsof the aromatic polyamide fiber is extremely low in bending rigidity.Although the bending rigidity can be improved by bonding said bundle offilaments together by the aid of a thermosetting plastic resin, theresultant tensile member is unfavorably increased in volume, weightratio and diameter ratio. In addition, the tenacity and tensile modulusof such a tensile member are considerably decreased in comparison withthose before bonding.

Besides, the aromatic polyamide fiber is still not enough in abrasionresistance and resistance to fatigue from flexing.

As a result of an extensive study, it has now been found that a filamentmade of ultra high molecular weight polyethylene and having a certaintenacity and a certain tensile modulus can provide a tensile member,particularly suitable as a reinforcing material for an optical fiber tomake an optical fiber cord or cable.

FIG. 1 is a diagram illustrating the relationship between temperatureand dynamic modulus for various filaments noted in Examples 1-7 andComparative Example 1;

FIG. 2 is a schematic view partially in cross section of a draw diethrough which a bundle of gel-like filaments are drawn;

FIG. 3 is a schematic view of a pair of squeezing rollers for squeezinga gel-like sheet;

FIG. 4 is a schematic view partially in cross section of a draw diethrough which a compressed gel-like sheet is drawn;

FIG. 5 is a cross section of filament in accordance with the presentinvention; and

FIG. 6 is a cross section of another filament in accordance with thepresent invention.

According to the present invention, there is provided a tensile membercomprising at least one polyethylene filament having a viscosity averagemolecular weight of not less than 200,000, a tenacity of not less than20 g/d and a tensile modulus of not less than 600 g/d. There is alsoprovided an optical fiber cord or cable comprising at least one opticalfiber and at least one tensile member for reinforcing said opticalfiber, said tnesile member comprising at least one polyethylene filamenthaving a viscosity average molecular weight of not less than 200,000, atenacity of not less than 20 g/d and a tensile modulus of not less than600 g/d.

Conventional polyethylene fibers are usually prepared by a melt spinningprocedure without using any solvent. With increase of the degree ofpolymerization, the melt viscosity is markedly enhanced so that thespinning operation becomes difficult. Also the increase of the degree ofpolymerization makes the molecular chain of polyethylene longer, and theentanglement among the molecular chains is thus increased. As theresult, a orientation of the molecular chains in a certain direction bydrawing after the spinning operation becomes difficult. Because of thisreason, the viscosity average molecular weight of polyethylene to bemelt spun is restricted to be less than 200,000. In the presentinvention, polyethylene to be used has a viscosity aberage molecularweight of not less than 200,000 and is formed in filaments by a certainspecific procedure as hereinafter explained so that the resultantfilaments can have high tenacity and high tensile modulus.

As stated above, polyethylene to be used in this invention should have aviscosity average molecular weight of not less than 200,000, preferablynot less than 300,000, more preferably not less than 500,000, the mostpreferably not less than 1,000,000. A larger viscosity average molecularweight is better, because higher tenacity and higher tensile modulus canbe attained. Thus, no upper limit is present on the viscosity averagemolecular weight. Usually, however, it may be not more than 10,000,000,particularly not more than 8,000,000, more particularly not more than6,000,000.

The polyethylene filament should have a tenacity of not less than 20g/d, preferably not less than 23 g/d, more preferably not less than 25g/d, and a tensile modulus of not less than 600 g/d, preferably not lessthan 700 g/d, more preferably not less than 800 g/d. When these physicalconstants are satisfied, the polyethylene filament can provide thetensile member with performances sufficient to use as an industrialtensile member, particularly a tensile member for optical fiber cord orcable which is required to have a tensile modulus of not less than5,000-7,000 kg/mm². When the tenacity is less than 20 g/d, a tensilemodulus of not less than 600 g/d can be hardly attained. In case of thetensile modulus being less than 600 g/d, the desired bending rigidity isnot obtainable so that the performances as required for an industrialtensile member can not be achieved. As understood from the abovedescriptions, higher tenacity and higher tensile modulus are better.From the practical viewpoint, however, the maximum values for tenacityand tensile modulus are ordinarily 60 g/d and 2,000 g/d, respectively.

In addition, the polyethylene filament is favorable to have a longperiod spacing of not less than 200 Å, particularly of not less than 300Å, although it is not essential.

With respect to the pure bending of an elastic bar onto which no shearforce acts, the following relationship is present: ##EQU1## wherein M isthe bending moment, E is the tensile modulus (Young's modulus), I is thesecondary moment at a section, R is the curvature radius at the mediatelayer of the bar and D is the diameter of the bar in case of having around section. Since the degree of bending rigidity corresponds to thebending moment, it is proportional to E and I of the product. I isdetermined by the geographical shape of the section of the bar. Theabove relationship is substantially applicable to the bending rigidityof a fiber or filament without any great error; i.e. the bendingrigidity of a fiber or filament is proportional to the tensile modulus(E) and influenced by the fourth power of the diameter of the fiber orfilament at a section.

Accordingly, the bending rigidity of a multi-filament (multiplefilaments) is small in comparison with that of a mono-filament (singlefilament) when they have a nearly equal denier. When the denier of eachfilment of a multi-filament is smaller and the number of the filamentsis increased, the multi-filament will be bent easier. When the denier ofeach filament is larger and the number of filaments is decreased, themulti-filament will be bent more difficulty.

In general, the tensile member having a higher bending moment, i.e. M inthe formula (1), is more favorable. Thus, the tensile modulus (E), whichis decided on the physical property of its material, is preferablylarger. The secondary moment at a section (I) may be decided dependingupon the purpose and use. When, for instance, the bending moment is thesame, the secondary moment at a section (I) is smaller with a largertensile modulus (E). In case of the material having a small density,there is obtainable a tensile member having a small section area, alight weight and a good handling property.

The filament has usually a section area of not less than 0.018 mm²,preferably not less than 0.030 mm², more preferably not less than 0.05mm². No particular upper limit is present, but it may be usually notmore than 180 mm², practically not more than 8.0 mm², more practicallynot more than 1.8 mm².

The tensile member of the invention is characteristically small invariation of the dynamic modulus with temperature. For instance, itaffords a E'₈₀ ° C/E'₂₀ ° C. value (i.e. the variation rate of thedynamic modulus at 80° C. to that at 20° C.) of not less than 60%,preferably not less than 70%, more preferably not less than 80%.Further, for instance, FIG. 1 in the accompanying drawings shows therelationship between dynamic modulus and temperatures for variousfilaments as obtained in Examples 1 to 7 and Comparative Example 1, fromwhich it may be understood that the filaments of the invention (A to G)are much smaller than the conventional filament of polyethylene (H) invariation of dynamic modulus within a range of 20 to 80° C. In otherwords, the tensile member of the invention shows only little depressionin modulus even under such a high temperature as 80° C. This is quiteadvantageous for practical use.

The performances required for the tensile member are varied with thepurpose and use. Usually, a tensile modulus of not less than 600 g/d mayassure that the tensile member will be practically usable for varioususes. When a tensile member is to be used for optical fiber cord orcable, the tensile modulus may be not less than 5,000-7,000 kg/mm². Asunderstood from the formula (1), a tensile member having too small asection area is not suitable because the desired bending rigidity ishardly obtained.

The tensile member of the invention satisfies said performances requiredfor industrial tensile members and is particularly suitable for opticalfiber cord or cable. The filament has usually a section area of not lessthan 0.018 mm², preferably not less than 0.030 mm², more preferably notless than 0.05 mm². In comparison with conventional metallic tensilemembers, it is advantageous in that it has a much lighter weight anddoes not have a problem of electromagnetic interference due to lightningstrikes.

For preparation of the filament in the invention, ultra high molecularweight polyethylene, i.e. polyethylene having a viscosity averagemolecular weight of not less than 200,000, preferably not less than300,000, more preferably not less than 500,000 the most preferably notless than 1,000,000, is spun in a solution state in a solvent, and theresultant gel-like filament is subjected to drawing in one or moresteps, preferably two or more steps, at a draw ratio of not less than10, preferably not less than 20. The resultant polyethylene filamentshows a tenacity of not less than 20 g/d, preferably not less than 23g/d, more preferably ably not less than 25 g/d, and a tensile modulus ofnot less than 600 g/d, preferably not less than 700 g/d, mor preferablynot less than 800 g/d. When the viscosity average molecular weight isless than 200,000, said high tenacity and/or tensile modulus are hardlyobtained.

Explaining said preparation procedure more in detail, ultra highmolecular weight polyethylene is dissolved in a solvent (e.g. decalin,xylene, paraffin) at a temperature lower than the boiling temperature ofthe solvent to make a polyethylene concentration of usually from 0.5 to50% by weight, preferably from 1 to 30% by weight. The resultingpolyethylene solution is extruded through a nozzle into the air or waterusually at room temperature. When desired, the polyethylene solution maybe extruded into a pipe equipped with a cooling apparatus. The resultantgel-like filament, which contains the solvent therein, is heated to atemperature at which said filament is not dissolved and drawn in one ormore steps at a draw ratio of not less than 10, preferably not less than20. In the above preparation procedure, the molecular chains ofpolyethylene are sufficiently extended in comparison with the molecularchains in the melt extrusion spinning process. Since the entanglement ofthe molecular chains is little in the spinning and/or solidified state,the drawing can be attained with a high draw ratio.

At the spinning step, a nozzle having a hole(s) of of appropriate sizeto give the filament(s) having a desired section area or denier may bechosen, and usually the one which can afford the filament(s) having 0.5denier (diameter at section, 0.0085 mm) or more is employed. When agel-like filaments extruded through the nozzle holes may be bundled,heated and drawn to give an integrally combined filament. Heating may bemade at such a temperature that the gel-like filaments are not readilycut. For the heating, there may be used a drawing apparatus with a hotplate, a heating apparatus of non-contact type with hot air or the like.A typical example of the draw die usable for this purpose is shown inFIG. 2. This Figure shows the enlarged schematic view of the section ofthe draw die, and O indicates the direction in which the filamentproceeds, P is a bundle of the gel-like filaments, Q is a draw die and dis the diameter of the hole of the draw die. The gel-like filaments (P)containing the solvent is supplied to the draw die (Q) having a conicalintroduction port are passed therethrough, whereby an integrallycombined filament is obtained.

Alternatively, the filament of the invention mahy be prepared bydissolving ultra high molecular weight polyethylene in a solvent andcooling the resultant solution to produce gel-like particles. Thegel-like sheet composed of gel-like particles is compressed to remove aportion of the solvent therefrom and then drawn, whereby a filament isobtained.

Explaining this procedure more in detail, ultra high molecular weightpolyethylene is dissolved in a solvent (e.g. decalin, liquid paraffin)while heating to make a polyethylene concentration of 0.5 to 15% byweight. The resulting solution is cooled so that gel-like particles ortheir collective blocks are formed. When desired, the gel-like particlesor their collective blocks are broken to make them finer. The resultantdispersion is filtered, for instance, by the use of a filtrationapparatus such as a paper machine to make a gel-like sheet. The gel-likesheet is squeezed, for instance, by passing through the gap between tworollers, which are disposed so as to apply a certain load thereto, toremove a portion of the solvent therefrom. A typical example of thesqueezing manner is shown in FIG. 3 wherein R and R' are rotatingrollers, S is a gel-like sheet and O indicates the direction in whichthe gel-like sheet proceeds. Namely, the gel-like sheet (S) is passedthrough the gap between two rotating rollers (R, R'), whereby thegel-like sheet (S) is compressed and simultaneously a portion of thesolvent is squeezed out. The thus compressed sheet is then drawn at aratio of not less than 20. On drawing, the use of a die with a holehaving an appropriate sectional shape can afford the filament of desiredsection shape such as round. The die as usable is provided preferablywith a hole having a section area smaller than that of the compressedsheet to be supplied thereto and a conical introducing port which makesdrawing easier. For die drawing, the compressed sheet as folded orrolled is supplied to the die and protruded through the die so heated asto carry out the drawing at an appropriate temperature (e.g. 90 to 130°C.) lower than the melting point of the supplied sheet. A typicalexample of the die is shown in FIG. 4. This Figure shows the enlargedschematic view of the section of the die, and O indicates the directionin which the compressed sheet proceeds, T is the compressed sheet, Q isthe die and d is the diameter of the hole of the die. The compressedsheet (T) containing the solvent is folded and supplied to the draw die(Q) having a conical introduction port and passed therethrough, wherebya shaped product having a round section is obtained. For obtaining thefilament of sufficiently high tensile modulus, the product as once drawnmay be further subjected to die drawing through a die having a hole ofsmaller section area than that of the hole in the die as previouslydrawn. Alternatively, the once drawn product may be subjected to heatdrawing without using a die.

The thus obtained filament has a section corresponding to the section ofthe hole of the die used. No crack is observed at the section. Thus, itis compact and of even quality and has a high tenacity of 20 g/d or moreand a high tensile modulus of 600 g/d or more. Further, it can have agreat section area.

As stated above, the filament is useful as a tensile member andparticularly suitable as a reinforcing material for an optical fiber tomake an optical fiber cord or cable. For this purpose, there may be usedone or more filaments. One typical example of the structure of theoptical fiber cord or cable is shown in FIG. 5. This Figure shows aschematic view of the section of the optical fiber cord; the jacketedoptical fiber (I) is located at the central portion and surrounded by amultiple number of the filaments of the invention to make a tensilemember layer (J), which is covered by a protective layer (K) made of aplastic material such as a vinyl chloride resin. Another typical exampleis shown in FIG. 6. This Figure shows a schematic view of the section ofthe optical fiber cable; the filament (J) of the invention as thetensile member is jacketed with a protective layer (L) made of a plasticmaterial such as a urethane resin and further surrounded by a multiplenumber of the optical fibers (I). The outside is covered by a protectivelayer (K) made of a plastic material such as polyethylene.

The tensile member of the invention has high tenacity and high tensilemodulus. It has a somewhat a larger diameter ratio (e.g. 1.20-1.86) thansteel wire and a much smaller weight ratio (0.18 to 0.42) than steelwire. Compared with the aromatic polyamide fiber, it is excellent inabrasion resistance and resistance to fatigue from flexing. Incomparison with steel wire and the aromatic polyamide fiber, it isexcellent in chemical resistance, particularly resistance to acidicsubstances. Therefore, those conventional tensile members are apt to bedeteriorated during their application in the air or under the ground,while no material deterioration is observed on the tensile member of theinvention. It is particularly notable that the tensile member of theinvention can be made in the one having a large section area with hightenacity and high tensile modulus. Thus, the bending rigidity isexcellent.

Practical and presently preferred embodiments of the invention areillustratively shown in the following Examples wherein part(s) and % areby weight unless otherwise indicated. Measurement of various physicalconstants was carried out in the following manner:

(1) Viscosity average molecular weight (Mv):

The viscosity was measured on the decalin solution at 135° C. accordingto the method as described in ASTM D2857 to determine the intrinsicviscosity [η], which was then introduced into the following equation tocalculate the viscosity average molecular weight (Mv):

    Mv=3.64×10.sup.4 ×[η].sup.1.39

(2) Tenacity:

Measured by the constant speed elengation method as described in JIS(Japan Industrial Standard) L1013 (1981).

(3) Tensile modulus:

Measured by the initial resistance to stretching method as described inJIS L1013 (1981).

(4) Diameter ratio and weight ratio of tensile member:

The diameter ratio and weight ratio of the tensile member weredetermined taking the diameter and weight of the steel wire having anearly equal tensile modulus (20,000 kg/mm²) to that of the tensilemember respectively as 1.

(5) Density:

Measured by the gradient density tube method as described in JIS L1013(1981), 7.14.2.

(6) Dynamic modulus E' (dyne/cm):

The dynamic modulus E' was measured from 20 to about 160° C. whileheating with a driving frequency of about 110 Hz and a temperatureelevation rate of about 1° C./mm² by the use of a direct reading dynamicvisco-elastic tester "VIBRON" Model DDV-II or "RHEOVIBRON" Model DDV-III(manufactured by Toyo Sokki) to obtain the dynamic modulus-temperaturecharacteristics.

The dynamic modulus at 80° C. (E'₈₀ ° C.) and at 20° C. (E'₂₀ ° C.) asdetermined above were introduced into the following formula to obtainthe E'₈₀ ° C./E'₂₀ ° C. rate (%):

    (E'.sub.80 ° C./E.sub.20 ° C.)×100

(7) Long period spacing of fiber:

Using an X ray diffraction apparatus "Rotar Flex" (manufactured byRigaku Denki), the small angle X ray scattering strength curve wasmeasured under the following conditions, and the long period spacing wascalculated from the position of the peak:

Detector: PSPC (proportional counter probe manufactured by RigakuDenki);

Camera radius: 510 mm;

PSPC resolving power: 0.007°/ch

Tube voltage of X ray producing apparatus: 45 Kv

Tube current of X ray producing apparatus: 50 mA

First pinhole slit: 0.15 mm (diameter)

Second pinhole slit: 0.15 mm (diameter)

Size of beam stopper: 1.7 mm wide

Measurement time: 5 minutes

EXAMPLE 1

Polyethylene (Mv, 2 x 10⁶) was dissolved in decalin at 160° C. to make aspinning liquid having a polyethylene concentration of 5%. The spinningliquid kept at 130° C. was extruded through a nozzle having round holes,each hole having a diameter of 2 mm, into the air of room temperature,followed by cooling to make gel-like filaments. A bundle of seventeengel-like filaments was drawn in four steps at four differenttemperatures under which the gellike filaments were not cut. Namely,drawing was carried out under the following conditions to give a totaldraw ratio of 75:

    ______________________________________                                        Step       Temperature (°C.)                                                                    Draw ratio                                           ______________________________________                                        1st         80           5                                                    2nd        110           4                                                    3rd        130           2.5                                                  4th        140           1.5                                                  ______________________________________                                    

The drawn filaments gave an appearance of a monofilament due tomelt-combining, and the section of the monofilament was an oval shapeand had a sectional area of 0.0328 mm² (corresponding to a circle havinga diameter of 0.204 mm), a long axis of 0.22 mm and a short axis of 0.19mm. According to the denier method, it may be expressed as 287 denier.The characteristic values of the monofilament are as shown in Table 1wherein those of conventional steel wire and conventional syntheticfibers are also shown for comparison.

The monofilament of this Example is remarkably of light weight incomparison with conventional steel wire. Since it has such a largediameter as 287 denier, the bending moment is higher than those ofKevlar 29 and Kevlar 49. The dynamic modulus at 80° C. is 94.2% of thatat 20° C. In comparison with conventional polyethylene for manufactureof fibers as shown in Reference Example 1, it can keep the modulus at amuch higher temperature. The long period spacing was 550Å.

EXAMPLE 2

Polyethylene (Mv, 2×10⁶) was dissolved in decalin at 160° C. to make aspinning liquid having a polyethylene concentration of 6%. The spinningliquid kept at 130° C. was extruded through a nozzle having round holes,each hole having a diameter of 2.5 mm, into the air of room temperature,followed by cooling to make gel-like filaments. A bundle of sixty-threegel-like filaments was drawn in four steps at four differenttemperatures under which the gel-like filaments were not cut. Namely,drawing was carried out under the following conditions to give a totaldraw ratio of 65:

    ______________________________________                                        Step       Temperature (°C.)                                                                    Draw ratio                                           ______________________________________                                        1st         80           5.5                                                  2nd        110           3.8                                                  3rd        130           2.4                                                  4th        140           1.3                                                  ______________________________________                                    

The drawn filaments gave an appearance of a monofilament due toemtl-combining, and the section of the monofilament was an oval shapeand had a sectional area of 0.0271 mm² (corresponding to a circle havinga diameter of 0.587 mm), a long axis of 0.65 mm and a short axis of 0.53mm. According to the denier method, it may be expressed as 2362 denier.The characteristic values of the monofilament are as shown in Table 1wherein those of conventional steel wire and conventional syntheticfibers are also shown for comparison.

The monofilament of this Example has such a large diameter as 2362denier and it exhibits a high tenacity as well as a high tensilemodulus. The dynamic modulus at 80° C. is 89.3% of that at 20° C. andthe long period spacing is 530 Å.

EXAMPLE 3

Polyethylene (Mv, 1×10⁶) was dissolved in decalin at 160° C. to make aspinning liquid having a polyethylene concentration of 10%. The spinningliquid kept at 130° C. was extruded through a nozzle having round holes,each hole having a diameter of 2 mm, into the air of room temperature,followed by cooling to make gel-like filaments. A bundle of ninegel-like filaments was drawn in four steps at four differenttemperatures under which the gel-like filaments were not cut. Namely,drawing was carried out under the following conditions to give a totaldraw ratio of 72:

    ______________________________________                                        Step       Temperature (°C.)                                                                    Draw ratio                                           ______________________________________                                        1st         80           5.5                                                  2nd        110           4                                                    3rd        125           2.5                                                  4th        135           1.3                                                  ______________________________________                                    

The drawn filaments gave an appearance of a monofilament due tomelt-combiningl, and the section of the monofilament was an oval shapeand had a sectional area of 0.0361 mm² (corresponding to a circle havinga diameter of 0.214 mm), a long axis of 0.23 mm and a short axis of 0.20mm. According to the denier method, it may be expressed as 314 denier.The characteristic values of the monofilament are as shown in Table 1wherein those of conventional steel wire and conventional syntheticfibers are also shown for comparison.

The monofilament of this Example has an average molecular weight of1,000,000 and exhibits a high tenacity as well as a high tensilemodulus. The dynamic modulus at 80° C. is 85.4% of that at 20° C. andthe long period spacing is 480 Å.

EXAMPLE 4

Polyethylene (Mv, 5×10⁵) was dissolved in decalin at 160° C. to make aspinning liquid having a polyethylene concentration of 15%. The spinningliquid kept at 130° C. was extruded through a nozzle having round holes,each hole having a diameter of 2 mm, into the air of room temperature,followed by cooling to make gel-like filaments. A bundle of sevengel-like filaments was drawn in four steps at four differenttemperatures under which the gel-like filaments were not cut. Namely,drawing was carried out under the following conditions to give a totaldraw ratio of 60:

    ______________________________________                                        Step       Temperature (°C.)                                                                    Draw ratio                                           ______________________________________                                        1st         80           5                                                    2nd        110           4                                                    3rd        125           2                                                    4th        135           1.5                                                  ______________________________________                                    

The drawn filaments gave an appearance of a monofilament due tomelt-combining, and the section of the monofilament was an oval shapeand had a sectional area of 0.0509 mm² (corresponding to a circle havinga diameter of 0.255 mm), a long axis of 0.27 mm and a short axis of 0.24mm. According to the denier method, it may be expressed as 443 denier.The characteristic values of the monofilament are as shown in Table 1wherein those of conventional steel wire and conventional syntheticfibers are also shown for comparison.

The monofilament of this Example has an average molecular weight of500,000 and exhibits a high tenacity as well as a high tensile modulus.In order to afford the same tenacity as that of the conventional steelwire, the ratio of diameter and the weight ratio should become 1.66 and0.34, respectively. The dynamic modulus at 80° C. is 76.9% of that at20° C. and the long period spacing is 340 Å.

EXAMPLE 5

Polyethylene (Mv, 2.4×10⁵) was dissolved in decalin at 160° C. to make aspinning liquid having a polyethylene concentration of 18%. The spinningliquid kept at 130° C. was extruded through a nozzle having round holes,each hole having a diameter of 2 mm, into the air of room temperature,followed by cooling to make gel-like filaments. A bundle of elevengel-like filaments was drawn in four steps at four differenttemperatures under which the gel-like filaments were not cut. Namely,drawing was carried out under the following conditions to give a totaldraw ratio of 59:

    ______________________________________                                        Step       Temperature (°C.)                                                                    Draw ratio                                           ______________________________________                                        1st         80           7                                                    2nd        110           3.5                                                  3rd        125           2                                                    4th        135           1.2                                                  ______________________________________                                    

The drawn filaments gave an appearance of a monofilament due tomelt-combining, and the section of the monofilament was an oval shapeand had a sectional area of 0.0980 mm² (corresponding to a circle havinga diameter of 0.353 mm), a long axis of 0.39 mm and a short axis of 0.32mm. According to the denier method, it may be expressed as 846 denier.The characteristic values of the monofilament are as shown in Table 1wherein those of conventional steel wire and conventional syntheticfibers are also shown for comparison.

The monofilament of this Example has an average molecular weight of240,000, exhibits a high tenacity as well as high tensile modulus andshows a yarn size of 846 denier. The dynamic modulus at 80° C. is 67.2%of that at 20° C. and the long period spacing is 260 Å.

EXAMPLE 6

Polyethylene (Mv, 2×10⁶) was dissolved in decalin at 160° C. to make aspinning liquid having a polyethylene concentration of 4%. The spinningliquid kept at 130° C. was extruded through a nozzle having round holes,each hole having a diameter of 0.7 mm, into water of 30° C. to makegel-like filaments. A bundle of one hundreds and eighty gel-likefilaments, which contained decalin in 94.5% and a sectional area of eachfilament was 0.71 mm², were drawn 2 times in length by the aid of thedie as shown in FIG. 2 of the accompanying drawing and taken up. Thetemperature of the die was kept at 80° C. during the operation. Thedrawn gel-like filaments were passed through a hot-air bath of 130° C.so as to draw 8.8 times and further a hot-air bath of 140° C. so as todraw 2 times, the total draw ratio being 35, to obtain a drawn filamentsubstantially containing no decalin.

The thus drawn fiber gave an appearance of a monofilament due tomelt-combining, and the section of the monofilament was a round shapeand had a sectional area of 0.205 mm² (corresponding to a circle havinga diameter of 0.511 mm). According to the denier method, it may beexpressed as 1790 denier. The characteristic values of the monofilamentare as shown in Table 1.

The monofilament of this Example exhibits a high tenacity as well as ahigh tensile modulus. The dynamic modulus at 80° C. is 88.1% of that at20° C. and the long period spacing is 470 Å.

EXAMPLE 7

Polyethylene (Mv, 2×10⁶) was dissolved in decalin at 160° C. to make asolution having a polyethylene concentration of 3%. The resultantsolution was allowed to cool at room temperature for 10 hours to make agel-like material, followed by pulverization by the aid of a homomixer.The thus prepared material comprised gel-like particles and a solvent,the average particle size of the particles being 80 u. After removal ofthe solvent by filtration, the particles were allowed to stand on afilter cloth, whereby a gel-like sheet of 4 mm in thickness wasobtained. The gel-like sheet still contained the solvent, in which thepolyethylene concentration being 16%, and showed a melting point of 92°C. The gel-like sheet on the filter cloth was permitted to go throughbetween two metal rolls rotating at even speed under compression toeliminate the solvent, whereby a compressed sheet was obtained. Thediameter of the rolls was 150 mm, each rolls being spaced by a distanceof 0.7 mm, and a rotating speed was 7 times/minute. The compression wascarried out at room temperature (ca. 27° C.).

The compressed sheet contained polyethylene in a concentration of 48%,had a thickness of 0.6 mm and a width of 200 mm and showed a highstrength as not breaking even at bending. The sheet was supplied to adraw die while plaiting in a width of 15 mm for drawing and taken up ata speed of 0.5 m/minute. The draw die was provided with a roundsectional hole, of which the diameter and the length were respectively 4mm and 5 mm, and a cone-shaped conduit, the half angle of the cone being10°, of 40 mm in length and kept at 110° C.

The compressed sheet passed through the draw die was drawn 9.4 times inlengthwise direction and had a round section. Scarce crack on thesection could be found so that there hardly imagined that the compressedsheet was made from a sheet-like material.

The thus obtained compressed sheet was further permitted to go throughbetween a hot-air bath of 135° C. and subjected to a conventionaldrawing method under heating by the aid of two rolls having differentrotating speed so as to obtain a desired hard drawn monofilament, whichhad a round section of 1.1 mm. The characteristic values of themonofilament are as shown in Table 1.

Although the monofilament of this Example has a yarn size of 8,322denier, it exhibits a high tenacity as well as a high tensile modulus.The dynamic modulus at 80° C. is 87.2% of that at 20° C. and the longperiod spacing is 450 Å.

REFERENCE EXAMPLE 1

Polyethylene (Mv, 6.5×10⁴) was dissolved in decalin at 160° C. to make aspinning liquid having a polyethylene concentration of 50%. The spinningliquid kept at 130° C. was extruded through a nozzle having round holes,each hole having a diameter of 2 mm, into the air of room temperature,followed by cooling to make gel-like filaments. A bundle of gel-likefilaments was drawn in four steps at four different temperatures underwhich the gel-like filaments were not cut. Namely, drawing was carriedout under the following conditions to give a total draw ratio of 56:

    ______________________________________                                        Step       Temperature (°C.)                                                                    Draw ratio                                           ______________________________________                                        1st         80           8                                                    2nd        100           3                                                    3rd        120           1.8                                                  4th        130           1.3                                                  ______________________________________                                    

The drawn filaments had a sectional area of 0.0267 mm² (corresponding toa circle having a diameter of 0.184 mm), a long axis of 0.20 mm and ashort axis of 0.17 mm. According to the denier method, it may beexpressed as 230 denier. The characteristic values of the monofilamentare as shown in Table 1.

The average molecular weight of the monofilament of this Example is6.5×10⁴ and is inferior in tenacity and tensile modulus. The dynamicmodulus at 80° C. is 56.6% of that at 20° C. and the heat resistance ofthe filaments is not so good. The long period spacing is so short as 180Å.

                                      TABLE 1                                     __________________________________________________________________________            Average          Tensile                           Long                       molecular  Tenacity                                                                            modulus                                                                              Tensile member                                                                         Dynamic modulus                                                                           E' 80°                                                                       period                     weight                                                                              density kg/   kg/ Ratio of                                                                           Weight                                                                            (dyne/cm.sup.2)                                                                           E' 20°                                                                       spacing                    (--Mv)                                                                              (g/cm.sup.3)                                                                       g/d                                                                              mm.sup.2                                                                         g/d                                                                              mm.sup.2                                                                          diameter                                                                           ratio                                                                             E' 80° C.                                                                    E' 20° C.                                                                    (%)   (Å)            __________________________________________________________________________    Steel wire                                                                            --    7.81  5 350                                                                               285                                                                             20000                                                                             1    1   --    --    --    --                 Kevlar 29                                                                             --    1.44 25 325                                                                               478                                                                              6200                                                                             1.8  0.6 --    --    --    --                 Kevlar 49                                                                             --    1.44 21 270                                                                              1000                                                                             13000                                                                             1.24 0.28                                                                              --    --    --    --                 Polyester fiber                                                                       --    1.38  8 100                                                                               161                                                                              2000                                                                             3.2  1.8 --    --    --    --                 Nylon fiber                                                                           --    1.14  9  92                                                                               49                                                                               500                                                                              6.3  5.8 --    --    --    --                 Polyethylene                                                                          --    0.96  9  78                                                                               98                                                                               850                                                                              4.9  2.9 --    --    --    --                 fiber                                                                         Example 1                                                                             2 × 10.sup.6                                                                  0.973                                                                              44 385                                                                              1590                                                                             13924                                                                             1.20 0.18                                                                              1.30 × 10.sup.12                                                              1.38 × 10.sup.12                                                              94.2  550                Example 2                                                                             2 × 10.sup.6                                                                  0.970                                                                              40 349                                                                              1250                                                                             10913                                                                             1.35 0.23                                                                              1.00 × 10.sup.12                                                              1.12 × 10.sup.12                                                              89.3  530                Example 3                                                                             1 × 10.sup.6                                                                  0.968                                                                              34 296                                                                              1120                                                                              9757                                                                             1.43 0.25                                                                              8.20 × 10.sup.11                                                              9.60 × 10.sup.11                                                              85.4  480                Example 4                                                                             5 × 10.sup.5                                                                  0.963                                                                              28 243                                                                               840                                                                              7280                                                                             1.66 0.34                                                                              5.57 × 10.sup.11                                                              7.24 × 10.sup.11                                                              76.9  340                Example 5                                                                             2.4 × 10.sup.5                                                                0.060                                                                              21 181                                                                               670                                                                              5789                                                                             1.86 0.42                                                                              3.85 × 10.sup.11                                                              5.73 × 10.sup.11                                                              67.2  260                Example 6                                                                             2 × 10.sup. 6                                                                 0.970                                                                              35 301                                                                               962                                                                              8400                                                                             1.54 0.30                                                                              7.31 × 10.sup.11                                                              8.30 × 10.sup.11                                                              88.1  479                Example 7                                                                             2 × 10.sup.6                                                                  0.973                                                                              24 210                                                                               680                                                                              6042                                                                             1.82 0.41                                                                              5.23 × 10.sup.11                                                              6.00 × 10.sup.11                                                              87.2  450                Reference                                                                             6.5 × 10.sup.4                                                                0.958                                                                              11  95                                                                               203                                                                              1750                                                                             3.38 1.40                                                                               9.9 × 10.sup.10                                                              1.75 × 10.sup.11                                                              56.6  180                Example 1                                                                     __________________________________________________________________________

What is claimed is:
 1. A drawn polyethylene filament having a viscosityaverage molecular weight of not less than 200,000, a tenacity of notless than 20 g/d, a tensile modulus of not less than 600 g/d, and asection area of not less than 0.018 mm².
 2. The drawn polyethylenefilament according to claim 1, wherein the viscosity average molecularweight is not less than 300,000.
 3. The drawn polyethylene filamentaccording to claim 1, wherein the viscosity average molecular weight isnot less than 500,000.
 4. The drawn polyethylene filament according toclaim 1, wherein the viscosity average molecular weight is not less than1,000,000.
 5. The drawn polyethylene filament according to claim 1,wherein the tenacity is not less than 23 g/d.
 6. The drawn polyethylenefilament according to claim 1, wherein the tenacity is not less than 25g/d.
 7. The drawn polyethylene filament according to claim 1, whereinthe tensile modulus is not less than 700 g/d.
 8. The drawn polyethylenefilament according to claim 1, wherein the tensile modulus is not lessthan 800 g/d.
 9. The drawn polyethylene filament according to claim 1,wherein the section area is not less than 0.03 mm².
 10. The drawnpolyethylene filament according to claim 1, wherein the section area isnot less than 0.05 mm².
 11. The drawn polyethylene filament according toclaim 1, which has a variation rate of dynamic modulus at an elevatedtemperature (E'₈₀ ° C.) to that at room temperature (E'₂₀ ° C.) is notless than 60%.
 12. The drawn polyethylene filament according to claim11, wherein the variation rate of the dynamic modulus is not less than70%.
 13. The drawn polyethylene filament according to claim 1, which isa polyethylene filament having a viscosity average molecular weight ofnot less than 200,000, a tenacity of not less than 20 g/d, a tensilemodulus of not less than 600 g/d, and a section area of from 0.018 to180 mm².
 14. A drawn polyethylene filament as set forth in claim 13,which is prepared by compressing a gel-like sheet prepared from asolution of polyethylene having a viscosity average molecular weight ofless than 200,000 in a solvent at a temperature lower than thedissolving temperature of the gel-like sheet to remove a portion of thesolvent contained therein and drawing the compressed sheet.